Digital oscilloscopes are powerful tools for analyzing waveforms. By digitizing one or more analog signals and storing the resulting digital values in memory the operator of the digital oscilloscope can leisurely peruse a persistent waveform display created from those stored values to investigate relationships of interest. Unlike an analog scope that cannot begin to write its display until it is triggered, its digital counterpart can retain data acquired prior to being triggered, and can thus display events both before and after the trigger event. Since any collection of memory is finite, the memory is generally organized to store the most recent samples at the expense of overwriting the oldest samples, and the operator specifies ahead of time what portion of the memory is to be used for data acquired subsequent to the trigger event, such that the events of interest are likely to be recorded in memory. The memory can be quite large, and might contain perhaps a thousand times more data than can be conveniently displayed. This leads to the notion of the displayed view as a scalable and positionable subset of the total data set. Panning is the name given to the operation of positioning the displayed subset, and zooming refers to the scale used to create that displayed view. So, for example, if there are two milliseconds of data in the memory, sampled at one nanosecond intervals, then there are two million samples for each channel that has been sampled. At even a moderately fast display scaling of, for example, 10 us/div, the ten divisions of the oscilloscope display will thus show only five percent of the acquired data. Panning and zooming must therefore be performed to identify meaningful views within the acquisition.
It often happens that it is desirable to visit and re-visit the different meaningful views several times, often in an arbitrary order, as questions arise and discussion ensues. And although there are various annunciators that indicate where in overall acquisition the present view is located, and what its horizontal and vertical scale are, with conventional equipment it is often inconvenient to alternately visit the different views of interest. Much manipulation of the controls is required, and there is the possibility of operator error. In addition, data is often stored off-line in a file and revisited over long periods of time. This necessitates the manual recording of position and scale parameters for those views that are of interest, lest they be forgotten and need to be discovered all over again. Such manually kept records can be misplaced or confused with other records, and are generally inconvenient. It would be desirable if the oscilloscope itself could assist in the process of identifying, cataloging and restoring views of interest within a stored trace acquisition.